The present invention relates to a magnetic recording medium having a two-component overlayer, including an metallic interlayer and a carbon overcoat. The medium is of the type formed on a rigid disk for use in magnetic recording devices, such as a computer disk drive.
Thin-film magnetic disks or media are widely used as data storage media for digital computers. These disks are typically formed by successively sputtering, onto a rigid disk substrate, an underlayer, a magnetic recording layer, and a carbon overcoat. The carbon overcoat protects the magnetic layer from wear, reduces the frictional forces between the disk and the read/write head, and protects the magnetic medium against environmental corrosion.
The continued growth in the storage capacity and recording density of thin film media requires reduction of the magnetic spacing between the head and the disk, with such spacing currently approaching less than one microinch. One approach to reducing magnetic spacing is reducing the thickness of the disk overcoat. A thin overcoat allows the head to fly closer to the magnetic film layer, which leads to improved magnetic recording properties. However, sputtered thin carbon overcoats, e.g., less than about 100 xc3x85, do not generally provide adequate protection against wear and particularly against corrosion. A carbon coat overlying an intermediate silicon layer has been described (Meyerson et al., U.S. Pat. No. 4,647,494). However, these systems typically used relatively thick carbon layers (e.g. 250-400 xc3x85), which impair magnetic recording performance, and they would not be expected to show adequate wear resistance or corrosion resistance at thicknesses less than 100 xc3x85. It is therefore desirable to provide an overlayer material for such disks which is effective at thicknesses less than 100 xc3x85.
In one aspect, the invention provides a two-component protective overlayer for a magnetic recording medium. The medium is of the type having a nonmagnetic, rigid disk substrate which supports a magnetic recording layer, typically including a nonmagnetic underlayer between the substrate and recording layer. The overlayer includes a protective carbon overcoat, and, between the magnetic recording layer and the carbon overcoat, a nonmagnetic metallic interlayer. The metallic interlayer is composed of a transition metal-silicon alloy or a transition metal-germanium alloy. Preferred transition metals include Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zr, Nb, Mo, Rh, Pd, Ta, W, Re, Os, and Ir. Particularly preferred transition metals are those, such as nickel, which form silicon or germanium alloys which bond well with cobalt or cobalt alloys. An exemplary compound is nickel-silicon alloy.
Preferably, the interlayer and carbon overcoat form a thin layer, having a combined thickness of about 40-100 Angstroms, and more preferably about 50-90 Angstroms. The carbon overcoat component preferably has a thickness of at least 30 Angstroms, while the metallic interlayer preferably has a thickness of at least 10 Angstroms.
The invention also provides a magnetic recording medium having such a two-component overlayer. The medium includes a nonmagnetic, rigid disk substrate, a nonmagnetic underlayer formed on the substrate, a magnetic recording layer, a protective carbon overcoat, and, between the magnetic recording layer and the carbon overcoat, a nonmagnetic metallic interlayer as described above. The magnetic recording layer is preferably composed of a cobalt alloy.
The invention also provides a method of forming a thin, wear-resistant and corrosion resistant overlayer on a rigid disk substrate, where the substrate preferably has a magnetic layer composed of a cobalt alloy. According to the method, an interlayer of a transition metal-silicon alloy or germanium alloy, having a thickness of about 10 to 40 Angstroms, is applied onto the magnetic layer, followed by the application of a carbon overcoat, having a thickness of about 30 to 60 Angstroms, onto the interlayer. The metallic interlayer is typically applied by sputter deposition from a target containing an alloy or intermetallic compound of a transition metal with silicon or germanium. The carbon overcoat may be applied by sputter deposition, ion beam deposition, or chemical vapor deposition, and may be doped with hydrogen and/or nitrogen.